Modern fermentation processes used for the production of wine, cider, beer, sake, potable ethanol and other fermentation products include the use of selected yeasts. Selected yeasts are made commercially available to the producer in dry forms, either as vermicellae (Instant Dry Yeast IDY) or pellets (Active Dry Yeast ADY). These dry forms are standard in the yeast industry as they allow long term storage while keeping a very high viability in the range 1 to 3×1010 colony forming units per gram of dry products. Commercial dry yeasts include more than 500 different strains. Most of them belong to Saccharomyces genus and a few to other geni such as Torulaspora, Metschnikowia, Pichia or Candida. 
The use of a selected yeast strain is an essential quality step in modern winemaking and other fermentation industries. For winemaking, grapes are crushed or pressed to release a grape must. As harvested grapes are not pasteurised and sterilized, they contain a vast population of indigenous (or wild) yeasts of different genii. Yeast cells of the selected commercial strain compete with this indigenous flora. It is therefore essential for the winemaker to ensure a “successful implantation” of the selected yeast strain. This means that the commercial yeast must be added with adequate viability so that it becomes predominant among naturally occurring yeasts in the fermentation media. It is accepted in the fermentation industry, and especially in the winemaking industry, that such yeasts must be added after a careful rehydration step. The objective of rehydration is to achieve the maximum viability (expressed as the percentage of live cells) immediately prior to introduction of the rehydrated yeast into the grape must. Rehydration is dealt with extensively in the article entitled “Rehydration Protocols for Active Dry Wine Yeasts and the Search for Early Indicators of Yeast Activity” published in Am. J. Enol. Vitic. 57:4 (2006). Applicant is not aware of any disclosure of any procedure which does not include the rehydration step with all its inherent difficulties that are known to winemakers worldwide.
Standard rehydration includes the following steps:                Preparation of a water solution at 37 to 40° C. in a rehydration receptacle (a bucket or a small tank). Sugar or grape must is added to reach 40 g/l of sugar;        Addition of ADY or IDY to this warm solution with continuous stirring;        mixing (gentle to vigorous);        the solution stands for 20 min to achieve rehydration. Formation of foam due to the production of CO2 is visible at this stage;        preferably the solution is diluted progressively using grape must from the tank to be fermented. This is to avoid a temperature shock if there is a large difference with respect to the cold must;        addition to fermentation tank (the temperature of the must is generally in the range 10-25° C. at this stage).        
This standard rehydration process is common industry practice. However it has a number of drawbacks:                It is tedious and time consuming in a busy period for winemakers;        Following all steps is complex and often not followed in practice;        The procedure is not convenient for large quantities of yeast (above 50 kg);        The rehydration vessels have to be cleaned thoroughly between successive rehydration processes to avoid cross-contamination between fermentation tanks when different yeast strains are used;        Considerable time is needed to complete the procedure;        Water is consumed;        When the procedure is not followed properly, the viability of the yeast is low and successful of implantation of the selected strain cannot be guaranteed.        
One object of the present invention is to provide a method of, and apparatus for, delivering dry yeast (ADY or IDY) to a fermentation tank. A further object is to provide a yeast formulation incorporating additives for delivery to a fermentation tank.